Pisan calendar
The calendar in use in Pisa from the Middle Ages until at least 1406 began on 25 March in the year of Jesus' incarnation. This method of dating was followed also in Cortona and Pistoia. Dates in the Pisan calendar are said to be in the stile pisano or by the calculus Pisanus. The calendar belonged to the stile dell'Annunciazione, which began the year with the Feast of the Annunciation, in contrast to those of the stile della Natività, which began the year with Christmas, like the calendars in use in Arezzo, Assisi and Perugia. The Florentine calendar, as well as that of Siena, also belonged to the stile dell'Annunciazione, but year one began one year after Jesus' incarnation.
In general, it is necessary to subtract one year from a date given in the Pisan calendar to obtain one given in the standard Gregorian calendar. This does not apply to dates between 1 January and 24 March inclusive, which are given in the same year in both calendars but consist in the final days of the Pisan calendar and the first of the Gregorian.
